MAXMATCH-23190028-src.cpp

#include<bits/stdc++.h>
using namespace std;
using cd = complex<double>;
#define pb push_back
#define nfs_mw ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
double PI = acos(-1);
int next_pow2(int no) { for(int i=0;i<6;i++) no |= no>>(1<<i);   return (no+1); }

void fft(vector<cd>& pol, int inv = 1)
{
	int n = pol.size(),i;
	if(n==1) return;
	
	vector<cd> e,o;
	
	for(i=0; i<n; i += 2) {	 e.pb(pol[i]);  o.pb(pol[i+1]); }
	
	fft(e,inv);
	fft(o,inv);

	cd w[n];

	for(i=0; i<n/2; i++) w[i] = cd(cos((2*PI*i*inv)/n),sin((2*PI*i*inv)/n));
	for(i=0; i<n/2; i++) pol[i] = e[i] + w[i]*o[i];
	for(i=0; i<n/2; i++) pol[i+(n/2)] = e[i] - w[i]*o[i];
	return;

}

void print(vector<cd> poly,int n)
{
	for(int i=n-1; i>=0; i--) cout<<((long long)round(poly[i].real()))<<" "; cout<<"\n";
}

vector<cd> polymul(vector<cd> a, vector<cd> b)
{
	int n = next_pow2( a.size() + b.size() - 1 ),i;
	a.resize(n,cd(0.0, 0.0));	b.resize(n,cd(0.0, 0.0));
	fft(a);
	fft(b);
	
	vector <cd> fab;
	transform(a.begin(), a.end(), b.begin(), back_inserter(fab), multiplies<cd>());
	
	fft(fab,-1);
	for(i=0; i<n; i++) fab[i] /= n;
	return fab;
}

int main()
{
	nfs_mw
	int i,j,maxm = 0,l,c;
	string s;
	cin>>s; l=s.length();
	vector<int> out;
	vector <cd> pol[3][3];
	for(i=0; i<3; i++) for(j=0;j<2;j++) pol[i][j].resize(l,cd(0.0,0.0));
	for(i=0 ;i<l; i++){
		c = s[i]-'a';
		pol[c][0][i] = cd(1.0,0.0);
		pol[c][1][l-1-i] = cd(1.0,0.0);
	}
	for(i=0;i<3;i++)
		pol[i][2] = polymul(pol[i][0],pol[i][1]);
	for(i=l; i<2*l; i++){
		int tmp=0;
		for(j=0;j<3;j++) tmp += round(pol[j][2][i].real());
		if(tmp>maxm){
			maxm = tmp;
			out.clear();
		}
		if(tmp==maxm) out.pb(i-l+1);
	}
	cout<<maxm<<"\n";
	for(auto v:out) cout<<v<<" ";
	cout<<"\n";
}